There are many biochemical as well as functional tests available to assess human zinc nutriture. However, it is generally agreed that no unequivocal test has been developed to accurately reflect zinc nutritional status in humans. Over 200 zinc metalloenzymes are known, and many of these have important roles in maintaining normal biochemical functions and structural integrity in humans. Angiotensin-converting enzyme (ACE) is a zinc metalloenzyme which converts angiotensin I to angiotensin II. Recent reports indicate that ACE activity is lower in zinc-deficient rats than in zinc-supplemented controls. These studies also demonstrated that ACE activity is increased by in vitro addition of zinc and that the % increase in activity (ACE activity stimulation ) is larger in zinc-deficient rats than in controls. Humans with low plasma serum levels of zinc have lower ACE activities. Our preliminary results indicate that in vitro zinc addition restores ACE activity of dialyzed human plasma which had lost over 75% of the activity. These findings suggests that an assay of ACE activity stimulation by in vitro addition of zinc may be used as a non-invasive functional test to assess zinc nutritional status in humans. We will test the hypothesis that the ACE activity stimulation is a sensitive and specific method to assess human zinc nutriture. The objectives of this proposal are: 1) to establish the optimal conditions for the assay of ACE activity stimulation, and 2) to validate this method using plasma obtained from subjects participating in a project entitled "Randomized trial of zinc supplementation during pregnancy" (1R01 HD27289; to be funded in 1990). This clinical trial is a randomized double-blind study to evaluation the effect of zinc supplementation on fetal growth. Two levels of zinc (20 or 40 mg per day) or a placebo will be given daily to pregnant black women beginning at 16-18 weeks gestation. The subjects will have low zinc nutriture, as assessed by measuring plasma zinc levels, but will be otherwise healthy. Plasma, leukocytes and erythrocyte zinc, alkaline phosphatase activity, and retinol-binding protein levels will be monitored. The subject will be divided in two groups, one receiving supplemental zinc, and the other placebo. Access to this population will provide us with an excellent opportunity to evaluate the proposed ACE in vitro stimulation of activity by zinc as a method for assessing zinc nutriture in humans.